Field of the Invention
This invention relates to an apparatus for separating blood into serum and clot phases by centrifugal separation.
Description of the Prior Art
Heretofore has been known a device for separating blood containing a thixotropic gel-like sealant, for example, a mixture consisting of silicone oil, silica and a gelling agent, at the bottom of a blood-collecting tube (U.S. Pat. No. 3,780,935). A volume of blood is collected in the blood-separation tube and, after being allowed to stand for an appropriate period of time, is subjected to centrifugal separation. The centrifugal force induces flow of the sealant and, due to its specific gravity being intermediate between serum and the clot portion, the sealant is gradually moved upward from the bottom of the tube eventually to a position intermediate the serum and clot layers, thereby enabling separation of the serum and clot layers. Such method, however, requires a considerably large centrifugal force, for example, 1500 G, when serum is to be separated from a small amount of blood. The large centrifugal force will cause injuries to blood cells to cause hemolysis, and it is occasionally problematic that correct biochemical test data cannot be obtained. The problem is especially influential when the gel-like material is made of a substance in which hardening of the gel proceeds with elapse of time due, for example, to formation of hydrogen bonds and which is liable to deterioration in flow behaviors.
In order to overcome the above-mentioned problem, a blood-separation tube has been devised in which the sealant as described above has a slant surface so that the sealant is readily flowable upon centrifugal separation (U.S. Pat. No. 3,997,442).
In such prior-art blood-separation tube, however, it is necessary in order to produce satisfactory flowability to have the upper surface of the sealant being slant at a considerably large angle. The upper surface slanted at a larger angle will suffer from a deficiency of being broken during transportation or handling of the product. It is also disadvantageous that the manufacturing line for forming such a slant surface is complex and costly because it requires an operation, for example, centrifugal operation which should be carried out not on a continuous basis but on a batch basis.
The sealant consisting of silicone oil, silica and a gelling agent is also associated with problems. It is produced by mechanically mixing the components which are poorly compatible one another and in which the gelling agent promotes formation of a hydrogen bond between silica particles (a specific gravity-adjusting agent) to produce thixotropic gel. It is therefore a matter of concern that the hydrogen bond becomes stronger as time elapses eventually to cohesion which results not only in phase segregation but also in poor flowability during the centrifugal operation. Whereas it has been proposed that a surfactant is incorporated to prevent the phase segregation, the ionic surfactant, if incorporated in a large portion, will produce another problem of hemolysis.
Moreover, other problems associated with the prior art compositions are that, when the above-cited composition is subjected to .gamma.-ray sterilization while contained in an appropriate amount in a blood-collecting tube, a marked change in character is induced, for example, by cross-linking to deteriorate performance as the sealant, that low-molecular substances in the gel-like material evaporate to make the inner surfaces of the tube water-repellent thereby bringing about delay in blood coagulation and adhering the clots to the inner surface, and that the raw materials are relatively expensive.
In addition to the above, a sealant consisting of a gel-like material based upon a polyester is known. As with the above-described prior-art gel-like materials, however, the sealant is also associated with problems such as delay in blood coagulation and clot adherence due to water-repellency on the inner surface of the tube made by the sealant as well as unpleasant odor produced.
It is therefore an object of this invention to provide a novel and improved apparatus for separating blood free from such disadvantages as set forth above.